import cv2
import numpy as np

img = cv2.imread('../images/lena.png')

plot = np.zeros(img.shape, np.uint8) + 255

cv2.circle(
    plot,
    (img.shape[1] // 2, img.shape[0] // 2),
    200,
    (0, 0, 0),
    -1)

plot = cv2.add(img, plot)

cv2.imshow('plot', plot)
cv2.imshow('img', img)
cv2.waitKey(0)